By default we choose /usr/bin/env python3 and suggest users specify a custom specific version. If you'd like to use "whatever is better than X" you could say "3.5 is fine, but use 3.6 if available" so it works even if 3.5 is not available...
Ok, so we're now (dfa362573ae6a448ff094b225c3af74fae515030 and c0c23a732aa9595ba6c07e07414d969215c77bc9) automatically using the newest version of Python that we find.
By default we choose /usr/bin/env python3 and suggest users specify a custom specific version. If you'd like to use "whatever is better than X" you could say "3.5 is fine, but use 3.6 if available" so it works even if 3.5 is not available...